Connected: An Internet Encyclopedia
RFC 1421 - 4.6 Summary of Encapsulated Header Fields

Top: Connected: An Internet Encyclopedia
Up: Requests For Comments
Up: RFC 1421
Up: 4. Processing of Messages
Prev: 4.5 Mail for Mailing Lists
Next: 4.6.1 Per-Message Encapsulated Header Fields

### 4.6 Summary of Encapsulated Header Fields

This section defines the syntax and semantics of the encapsulated header fields to be added to messages in the course of privacy enhancement processing.

The fields are presented in three groups. Normally, the groups will appear in encapsulated headers in the order in which they are shown, though not all fields in each group will appear in all messages. The following figures show the appearance of small example encapsulated messages. Figure 2 assumes the use of symmetric cryptography for key management. Figure 3 illustrates an example encapsulated ENCRYPTED message in which asymmetric key management is used.

       -----BEGIN PRIVACY-ENHANCED MESSAGE-----
       Proc-Type: 4,ENCRYPTED
       Content-Domain: RFC822
       DEK-Info: DES-CBC,F8143EDE5960C597
       Originator-ID-Symmetric: linn@zendia.enet.dec.com,,
       Recipient-ID-Symmetric: linn@zendia.enet.dec.com,ptf-kmc,3
       Key-Info: DES-ECB,RSA-MD2,9FD3AAD2F2691B9A,
                 B70665BB9BF7CBCDA60195DB94F727D3
       Recipient-ID-Symmetric: pem-dev@tis.com,ptf-kmc,4
       Key-Info: DES-ECB,RSA-MD2,161A3F75DC82EF26,
                 E2EF532C65CBCFF79F83A2658132DB47

       LLrHB0eJzyhP+/fSStdW8okeEnv47jxe7SJ/iN72ohNcUk2jHEUSoH1nvNSIWL9M
       8tEjmF/zxB+bATMtPjCUWbz8Lr9wloXIkjHUlBLpvXR0UrUzYbkNpk0agV2IzUpk
       J6UiRRGcDSvzrsoK+oNvqu6z7Xs5Xfz5rDqUcMlK1Z6720dcBWGGsDLpTpSCnpot
       dXd/H5LMDWnonNvPCwQUHt==
       -----END PRIVACY-ENHANCED MESSAGE-----

              Example Encapsulated Message (Symmetric Case)
                                Figure 2

Figure 4 illustrates an example encapsulated MIC-ONLY message in which asymmetric key management is used; since no per-recipient keys are involved in preparation of asymmetric-case MIC-ONLY messages, this example should be processable for test purposes by arbitrary PEM implementations.

Fully-qualified domain names (FQDNs) for hosts, appearing in the mailbox names found in entity identifier subfields of "Originator- ID-Symmetric:" and "Recipient-ID-Symmetric:" fields, are processed in a case-insensitive fashion. Unless specified to the contrary, other field arguments (including the user name components of mailbox names) are to be processed in a case-sensitive fashion.

In most cases, numeric quantities are represented in header fields as contiguous strings of hexadecimal digits, where each digit is represented by a character from the ranges "0"-"9" or upper case "A"-"F". Since public-key certificates and quantities encrypted

       -----BEGIN PRIVACY-ENHANCED MESSAGE-----
       Proc-Type: 4,ENCRYPTED
       Content-Domain: RFC822
       DEK-Info: DES-CBC,BFF968AA74691AC1
       Originator-Certificate:
        MIIBlTCCAScCAWUwDQYJKoZIhvcNAQECBQAwUTELMAkGA1UEBhMCVVMxIDAeBgNV
        BAoTF1JTQSBEYXRhIFNlY3VyaXR5LCBJbmMuMQ8wDQYDVQQLEwZCZXRhIDExDzAN
        BgNVBAsTBk5PVEFSWTAeFw05MTA5MDQxODM4MTdaFw05MzA5MDMxODM4MTZaMEUx
        CzAJBgNVBAYTAlVTMSAwHgYDVQQKExdSU0EgRGF0YSBTZWN1cml0eSwgSW5jLjEU
        MBIGA1UEAxMLVGVzdCBVc2VyIDEwWTAKBgRVCAEBAgICAANLADBIAkEAwHZHl7i+
        yJcqDtjJCowzTdBJrdAiLAnSC+CnnjOJELyuQiBgkGrgIh3j8/x0fM+YrsyF1u3F
        LZPVtzlndhYFJQIDAQABMA0GCSqGSIb3DQEBAgUAA1kACKr0PqphJYw1j+YPtcIq
        iWlFPuN5jJ79Khfg7ASFxskYkEMjRNZV/HZDZQEhtVaU7Jxfzs2wfX5byMp2X3U/
        5XUXGx7qusDgHQGs7Jk9W8CW1fuSWUgN4w==
       Key-Info: RSA,
        I3rRIGXUGWAF8js5wCzRTkdhO34PTHdRZY9Tuvm03M+NM7fx6qc5udixps2Lng0+
        wGrtiUm/ovtKdinz6ZQ/aQ==
       Issuer-Certificate:
        MIIB3DCCAUgCAQowDQYJKoZIhvcNAQECBQAwTzELMAkGA1UEBhMCVVMxIDAeBgNV
        BAoTF1JTQSBEYXRhIFNlY3VyaXR5LCBJbmMuMQ8wDQYDVQQLEwZCZXRhIDExDTAL
        BgNVBAsTBFRMQ0EwHhcNOTEwOTAxMDgwMDAwWhcNOTIwOTAxMDc1OTU5WjBRMQsw
        CQYDVQQGEwJVUzEgMB4GA1UEChMXUlNBIERhdGEgU2VjdXJpdHksIEluYy4xDzAN
        BgNVBAsTBkJldGEgMTEPMA0GA1UECxMGTk9UQVJZMHAwCgYEVQgBAQICArwDYgAw
        XwJYCsnp6lQCxYykNlODwutF/jMJ3kL+3PjYyHOwk+/9rLg6X65B/LD4bJHtO5XW
        cqAz/7R7XhjYCm0PcqbdzoACZtIlETrKrcJiDYoP+DkZ8k1gCk7hQHpbIwIDAQAB
        MA0GCSqGSIb3DQEBAgUAA38AAICPv4f9Gx/tY4+p+4DB7MV+tKZnvBoy8zgoMGOx
        dD2jMZ/3HsyWKWgSF0eH/AJB3qr9zosG47pyMnTf3aSy2nBO7CMxpUWRBcXUpE+x
        EREZd9++32ofGBIXaialnOgVUn0OzSYgugiQ077nJLDUj0hQehCizEs5wUJ35a5h
       MIC-Info: RSA-MD5,RSA,
        UdFJR8u/TIGhfH65ieewe2lOW4tooa3vZCvVNGBZirf/7nrgzWDABz8w9NsXSexv
        AjRFbHoNPzBuxwmOAFeA0HJszL4yBvhG
       Recipient-ID-Asymmetric:
        MFExCzAJBgNVBAYTAlVTMSAwHgYDVQQKExdSU0EgRGF0YSBTZWN1cml0eSwgSW5j
        LjEPMA0GA1UECxMGQmV0YSAxMQ8wDQYDVQQLEwZOT1RBUlk=,
        66
       Key-Info: RSA,
        O6BS1ww9CTyHPtS3bMLD+L0hejdvX6Qv1HK2ds2sQPEaXhX8EhvVphHYTjwekdWv
        7x0Z3Jx2vTAhOYHMcqqCjA==

       qeWlj/YJ2Uf5ng9yznPbtD0mYloSwIuV9FRYx+gzY+8iXd/NQrXHfi6/MhPfPF3d
       jIqCJAxvld2xgqQimUzoS1a4r7kQQ5c/Iua4LqKeq3ciFzEv/MbZhA==
       -----END PRIVACY-ENHANCED MESSAGE-----

        Example Encapsulated ENCRYPTED Message (Asymmetric Case)
                                Figure 3

using asymmetric algorithms are large in size, use of a more space- efficient encoding technique is appropriate for such quantities, and the encoding mechanism defined in Section 4.3.2.4 of this RFC, representing 6 bits per printed character, is adopted for this purpose.

Encapsulated headers of PEM messages are folded using whitespace per RFC 822 header folding conventions; no PEM-specific conventions are defined for encapsulated header folding. The example shown in Figure 4 shows (in its "MIC-Info:" field) an asymmetrically encrypted quantity in its printably encoded representation, illustrating the use of RFC 822 folding.

In contrast to the encapsulated header representations defined in RFC 1113 and its precursors, the field identifiers adopted in this RFC do not begin with the prefix "X-" (for example, the field previously denoted "X-Key-Info:" is now denoted "Key-Info:") and such prefixes are not to be emitted by implementations conformant to this RFC. To simplify transition and interoperability with earlier implementations, it is suggested that implementations based on this RFC accept incoming encapsulated header fields carrying the "X-" prefix and act on such fields as if the "X-" were not present.

       -----BEGIN PRIVACY-ENHANCED MESSAGE-----
       Proc-Type: 4,MIC-ONLY
       Content-Domain: RFC822
       Originator-Certificate:
        MIIBlTCCAScCAWUwDQYJKoZIhvcNAQECBQAwUTELMAkGA1UEBhMCVVMxIDAeBgNV
        BAoTF1JTQSBEYXRhIFNlY3VyaXR5LCBJbmMuMQ8wDQYDVQQLEwZCZXRhIDExDzAN
        BgNVBAsTBk5PVEFSWTAeFw05MTA5MDQxODM4MTdaFw05MzA5MDMxODM4MTZaMEUx
        CzAJBgNVBAYTAlVTMSAwHgYDVQQKExdSU0EgRGF0YSBTZWN1cml0eSwgSW5jLjEU
        MBIGA1UEAxMLVGVzdCBVc2VyIDEwWTAKBgRVCAEBAgICAANLADBIAkEAwHZHl7i+
        yJcqDtjJCowzTdBJrdAiLAnSC+CnnjOJELyuQiBgkGrgIh3j8/x0fM+YrsyF1u3F
        LZPVtzlndhYFJQIDAQABMA0GCSqGSIb3DQEBAgUAA1kACKr0PqphJYw1j+YPtcIq
        iWlFPuN5jJ79Khfg7ASFxskYkEMjRNZV/HZDZQEhtVaU7Jxfzs2wfX5byMp2X3U/
        5XUXGx7qusDgHQGs7Jk9W8CW1fuSWUgN4w==
       Issuer-Certificate:
        MIIB3DCCAUgCAQowDQYJKoZIhvcNAQECBQAwTzELMAkGA1UEBhMCVVMxIDAeBgNV
        BAoTF1JTQSBEYXRhIFNlY3VyaXR5LCBJbmMuMQ8wDQYDVQQLEwZCZXRhIDExDTAL
        BgNVBAsTBFRMQ0EwHhcNOTEwOTAxMDgwMDAwWhcNOTIwOTAxMDc1OTU5WjBRMQsw
        CQYDVQQGEwJVUzEgMB4GA1UEChMXUlNBIERhdGEgU2VjdXJpdHksIEluYy4xDzAN
        BgNVBAsTBkJldGEgMTEPMA0GA1UECxMGTk9UQVJZMHAwCgYEVQgBAQICArwDYgAw
        XwJYCsnp6lQCxYykNlODwutF/jMJ3kL+3PjYyHOwk+/9rLg6X65B/LD4bJHtO5XW
        cqAz/7R7XhjYCm0PcqbdzoACZtIlETrKrcJiDYoP+DkZ8k1gCk7hQHpbIwIDAQAB
        MA0GCSqGSIb3DQEBAgUAA38AAICPv4f9Gx/tY4+p+4DB7MV+tKZnvBoy8zgoMGOx
        dD2jMZ/3HsyWKWgSF0eH/AJB3qr9zosG47pyMnTf3aSy2nBO7CMxpUWRBcXUpE+x
        EREZd9++32ofGBIXaialnOgVUn0OzSYgugiQ077nJLDUj0hQehCizEs5wUJ35a5h
       MIC-Info: RSA-MD5,RSA,
        jV2OfH+nnXHU8bnL8kPAad/mSQlTDZlbVuxvZAOVRZ5q5+Ejl5bQvqNeqOUNQjr6
        EtE7K2QDeVMCyXsdJlA8fA==

       LSBBIG1lc3NhZ2UgZm9yIHVzZSBpbiB0ZXN0aW5nLg0KLSBGb2xsb3dpbmcgaXMg
       YSBibGFuayBsaW5lOg0KDQpUaGlzIGlzIHRoZSBlbmQuDQo=
       -----END PRIVACY-ENHANCED MESSAGE-----

         Example Encapsulated MIC-ONLY Message (Asymmetric Case)
                                Figure 4

4.6.1 Per-Message Encapsulated Header Fields

4.6.1.1 Proc-Type Field

4.6.1.1.1 ENCRYPTED
4.6.1.1.2 MIC-ONLY
4.6.1.1.3 MIC-CLEAR
4.6.1.1.4 CRL

4.6.1.2 Content-Domain Field
4.6.1.3 DEK-Info Field

4.6.2 Encapsulated Header Fields Normally Per-Message

4.6.2.1 Originator-ID Fields

4.6.2.1.1 Originator-ID-Asymmetric Field
4.6.2.1.2 Originator-ID-Symmetric Field

4.6.2.2 Originator-Certificate Field
4.6.2.3 MIC-Info Field

4.6.3 Encapsulated Header Fields with Variable Occurrences

4.6.3.1 Issuer-Certificate Field

4.6.4 Per-Recipient Encapsulated Header Fields

4.6.4.1 Recipient-ID Fields

4.6.4.1.1 Recipient-ID-Asymmetric Field
4.6.4.1.2 Recipient-ID-Symmetric Field

4.6.4.2 Key-Info Field

4.6.4.2.1 Symmetric Key Management
4.6.4.2.2 Asymmetric Key Management

Next: 4.6.1 Per-Message Encapsulated Header Fields

Connected: An Internet Encyclopedia
RFC 1421 - 4.6 Summary of Encapsulated Header Fields